In tire sound absorber

ABSTRACT

An in-tire sound absorber for a pneumatic wheel assembly including a wheel rim and a tire fitted to the wheel rim. The sound absorber is adapted to be located within a cavity defined by the wheel rim and the tire. The sound absorber comprises a first fibrous layer and a second fibrous layer. The second fibrous layer has a higher air flow resistance than the first fibrous layer. The first fibrous layer, the second fibrous layer, or both, is made from a non-woven fibrous web.

BACKGROUND

1. Technical Field

This invention relates to an in-tire sound absorber for the reduction oftonal sounds in pneumatic tires.

2. Description of the Related Art

Tonal sound is caused by a standing wave generated in the space betweenthe tire and wheel rim. This standing wave relates to the geometry ofthe tire, and the temperature and pressure of the air in the tirecavity. The resultant tone or sound is typically below 600 Hz.

The problem of tonal noise transmission into the motor vehicle cabinshas been addressed by a number of means. U.S. Pat. No. 6,755,483(Sumitomo Rubber Industries, Ltd.) describes the use of a noise damperdisposed in the cavity formed between the rim and the tire. The noisedamper is made from porous material which has a specific density ofbetween 0.005 and 0.06 and in particular an open-cell polyurethane foam.In one embodiment, the noise damper has an uneven facing, or is madefrom an outer layer having low sound reflection and an inner layer,adjacent the wheel rim, having high sound absorption.

However, it is often a problem with the prior art that the noise dampercan be damaged during fitment of the tire on the wheel rim or the noisedamper is not physically strong enough to resist tearing or breakingapart during normal operation.

BRIEF SUMMARY

It is an object of the invention to overcome, or at least ameliorate,some of the above problems or at least provide an alternative in-tiresilencer material and a system utilizing the in-tire silencer material.

Accordingly in one aspect, the present invention is an in-tire soundabsorber for a pneumatic wheel assembly including a wheel rim and a tirefitted to the wheel rim, the sound absorber comprising a first fibrouslayer and a second fibrous layer, the second layer having a higher airflow resistance than the first layer, and being configured to fit aroundthe wheel rim with the first layer in contact with a surface of thewheel rim and extending substantially between the second layer and thewheel rim.

The low air flow resistance of the first layer allows the standing soundpressure wave to propagate within the layer where the particle velocityof the radial pressure wave that creates the tonal noise is in a normaldirection to the direction of the pressure wave. The excited airparticles are thereby forced through the high air flow resistance of thesecond layer to provide the sound absorption.

Preferably the first and second layers are made from non-woven fibrouswebs. In a preferred embodiment, the first fibrous layer has fibersorientated substantially perpendicular to the surface of the wheel rim.The orientation substantially perpendicular to the surface of the wheelrim provides an increased tensile strength of the sound absorber in thedirection perpendicular to the surface of the wheel rim when contrastedwith conventional bulky non-woven fabrics in which the fibers arecross-lapped. This is particularly advantageous for embodiments wherethe centrifugal forces increase with the rotational speed of the wheelduring operation and the increased tensile strength in the directionperpendicular to the surface of the wheel rim decreases the risk ofdelamination of the sound absorber.

Preferably, the air flow resistance of the respective layers issubstantially consistent to provide a relatively constant acousticabsorption to reduce the tonal noise. In some embodiments, the ratio ofair flow resistance of the second layer to the first layer is between25:1 and 35:1. That is the air flow resistance of the second layer isbetween 25 and 35 times that of the first layer. In some embodiments,the ratio is approximately 30:1.

The spatial average of the air flow resistance of the second layer isbetween 400 and 1000 Rayls. In some embodiments, the spatial average isin the range of 600-800 Rayls.

The spatial average of the flow resistivity of the first layer is in therange of 800-8000 Rayls/m. In some embodiments, the spatial average is2000-4000 Rayls/m.

The first layer of the sound absorber can be made from a fibrous web ofpolyester fibers. In some embodiments, the second layer of the soundabsorber is made from a fibrous web of polyester fibers.

According to another aspect of the present invention, a tire soundabsorbing system includes a tire, a wheel rim, the wheel rim and tireforming an enclosed tire cavity, and a porous insert disposed adjacent asurface of the wheel rim within the tire cavity, the porous insertcomprising an inner fibrous layer proximal to the wheel rim surface andan outer fibrous layer distal to the wheel rim surface, the outerfibrous layer has a higher air flow resistance than the inner fibrouslayer, and wherein the porous insert is shaped to avoid damage duringfitment of the tire on the rim.

The porous insert is shaped so that the bead of the tire is able to pushaside the sound absorber during fitment so that damage to the soundabsorber is avoided. The porous insert has rounded edges to assist thetire bead in pushing the sound absorber to a position where the risk ofdamage is reduced. Even more preferably the rounded edges are formed bythermoforming. The rounded edges can be slit or notched to avoidcreasing of the porous insert.

The porous fibrous insert is removably attached to the wheel rim. A hookand loop attachment means is used wherein the loops are formed by theinner fibrous layer and the hooks are attached to the wheel rim.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Preferred embodiments of the present invention will now be described byway of example only with reference to the below figures.

FIG. 1 is a cross-sectional view of an in-tire sound absorber accordingto one embodiment of the invention.

FIG. 2 is a cross-sectional view of the in-tire sound absorbing systemusing the in-tire sound absorber of FIG. 1 installed on a wheel rim.

FIG. 3 is a cross-sectional view of an in-tire sound absorbing systemusing the in-tire sound absorber of FIG. 1 according to anotherembodiment.

FIG. 4A is a bottom plan view of a tongue and slot joining system forthe in-tire sound absorber of FIG. 1.

FIG. 4B is a cross-sectional view of a tongue and slot joining systemfor the in-tire sound absorber of FIG. 1.

FIG. 5 is a cross-sectional view of an in-tire sound absorber accordingto an alternative embodiment of the invention

FIG. 6A to 6C are graphs of the Noise versus Frequency of the testresults of Example 1.

DETAILED DESCRIPTION

Referring to FIGS. 1-4 the in-tire sound absorber 1 is comprised of afirst layer 3 of a thermoformable acoustic sheet, backed with a secondlayer 5 of a spacing layer of vertically lapped 3-dimensional thermallybonded non-woven fabric. The thermoformable acoustic sheet 3 islaminated to the vertically lapped fabric 5 using a thermoplasticadhesive 7 that is permeable. The sound absorber 1 is installed on awheel rim 9 to absorb at least some of the tonal noise of the tire.

The thermoformable acoustic sheet 3 is prepared generally in accordancewith the applicant's International patent application published as WO02/09089. The thermoformable acoustic sheet 3 is formed using polyesterfiber, has an air flow resistance between 400 and 1000 Rayls and a highresistance to tearing. Alternatively, the sheet 3 can be formed frompolypropylene or other suitable fiber. The sheet 3 has a thickness ofapproximately 0.5-1 mm, and a mass of approximately 50-250 g/m².

The vertically lapped fabric 5 is also made of polyester fibers. Anadvantage of the two layers 3, 5 being made of the same material is thatthe sound absorber 1 is recyclable. When installed the fibers in thefabric 5 are generally orientated in the radial direction because of thevertically lapped structure of the fabric 5. This provides additionalstrength to prevent separation of the sound absorber 1 due to thecentrifugal forces encountered during normal operation of the wheel. Theflow resistivity of the spacer layer 5 is less than that of thethermoformable acoustic sheet 3 and is between 800 and 8000 Rayls/m.

Prior to installation on the wheel rim 9, the edges 11 of thethermoformable acoustic sheet 3 are molded to provide a rounded edge tothe sound absorber 1 so that the risk of tearing of the sound absorber 1during fitment of the tire on the wheel rim 9 is reduced. This occursbecause the tire bead is able to push aside the sound absorber 1 duringfitment and there are no sharp edges to catch on. Thus it is possible toinstall a tire on the wheel rim 9 without damaging the sound absorber 1and without using a special groove in the wheel rim 9 to shelter theabsorber 1. The radius on the sound absorber edge 11 is typically in therange of 15-20 mm.

An added advantage of the rounded edges 11 and high tear resistance ofthe thermoformable acoustic sheet 3 is that the sound absorber 1 alsoresists damage from a tire lever during removal of the tire. This makesthe sound absorber 1 suitable for use on the wheel rim 9 with a numberof tires, prolonging the life of the sound absorber 1.

To provide the necessary sound absorption, the low air flow resistanceof the spacing layer 5 allows the standing sound pressure wave topropagate within the spacing layer 5. The particle velocity of theradial pressure wave that creates the tonal noise is in a normaldirection to the direction of the pressure wave. Thus the excited airparticles are forced through the high air flow resistance thermoformableacoustic sheet 3 which provides the sound absorption.

The sound absorber 1 is attached to the wheel rim 9 by an adhesive,mechanical fastening, or a combination of both. The adhesive, mechanicalfastening or combination must securely hold the sound absorber 1 inplace during replacement of the tire while still allowing the tire beadto push the sound absorber 1 aside during installation.

In the embodiment shown in FIG. 3, a hook and loop attachment means isused to attach the sound absorber 1 to the wheel rim 9. The verticallylapped spacer material 5 provides the loops and the hooks 13 areattached to the wheel rim 9. In this arrangement the sound absorber 1 isable to be replaced with another sound absorber if the sound absorber 1becomes ineffective or the tire on the wheel rim changes sufficientlythat a sound absorber with slightly different properties would be moresuited to the new configuration of the wheel rim 9 and tire.

In order to assist the attachment of the sound absorber 1 to the wheelrim 9, the two ends of the sound absorber 1 can be connected together byway of a fastening arrangement after the sound absorber has beenattached to the wheel rim 9. The fastening arrangement 14 shown in FIGS.4a and 4b uses a tongue 15 and slot 17 arrangement in the ends of thethermoformable acoustic sheet 3 to effectively form a torus around thewheel rim. An adhesive is also used to secure the sound absorber 1 ontothe wheel rim.

In an alternative embodiment, the two ends of the sound absorber may beconnected by a hook and loop fastening arrangement, wherein the hooksection is affixed to one end of the sound absorber by sewing, gluing orthermal staking, and the loop section is affixed to the other end bysimilar means.

Other methods of connecting the two ends of the sound absorber 1 may beemployed, without departing from the purpose of the invention, such asstapling, riveting, gluing.

In practical embodiments, the thickness of the sound absorber 1 isbetween 12 to 40 mm and more typically between 20 to 30 mm thick,although the thickness used in an actual installation will depend onphysical and acoustical requirements. The maximum practical height ofthe spacer layer 5 is normally about 25 mm.

The sound absorber 1 is normally between 50 to 150 mm wide dependingupon the shape and configuration of the wheel rim 9. However in mostwheel rims, the width is between 50 to 100 mm. The width of the soundabsorber 1 is generally kept to a minimum without affecting the soundabsorption as the wider the sound absorber, the more it affects fittingand removal of the tire. The preferred width is in the range of 70-100mm. At more than 100 mm wide, the likelihood of the tire bead catchingthe sound absorber 1 and may prevent the tire from sealing properly.

The sound absorber can be made to a length that is substantially equalto the circumference of the wheel rim, so that each wheel size requiresa different length. Alternatively, the length of the sound absorbercould be created by cutting excess material from a sound absorber of astandard length. In this embodiment, a fabric may be laminated on thesecond layer to provide the loops for a hook and loop fasteningarrangement where a hook section was attached to one end of the soundabsorber. In this arrangement, the hook and loop fastening arrangementcould be used regardless of the amount removed from the standard soundabsorber length.

In an alternative embodiment shown in FIG. 5, the edges 21 of the soundabsorber 23 are molded such that the second layer 25, a thermoformableacoustic sheet, extends along a substantial portion of the sides of thesound absorber 21. The extension of the thermoformable acoustic sheet 25along the sides of the sound absorber 21 increases the resistance of thesound absorber 21 to damage to the first layer 27, a vertically lappedfabric, during tire fitment.

As the curvature of sound absorber decreases with the thickness of thesound absorber when installed on the wheel rim, the edges of thethermoformable acoustic sheet 3 may be slit at regular intervals alongthe length of the sound absorber. This provides for overlapping of theedge at these intervals of the thermoformable to reduce the likelihoodof humps forming in the sound absorber and thereby making tire fitmentmore difficult. Alternatively, the edges of the thermoformable acousticsheet are notched. It should also be noted that the sound absorber maybe molded on a circular molding tool so that the curvature of the soundabsorber is substantially permanently molded into the sound absorber.

EXAMPLE 1

A prototype tire sound absorber, according to one embodiment of thisinvention with a lower air flow resistance spacer layer and a higher airflow resistance thermoformable acoustic sheet, was made up and attachedto alloy wheel rims using a pressure sensitive adhesive. Low profiletires were then fitted to the rim in the normal manner.

The alloy wheel rims were 18 inches diameter by 8 inches wide and thetires were Pontenza RE55S, 265/35ZR18.

The sound absorber measured 20 mm thick, 90 mm wide and molded with aradius on the leading edge.

The sound absorber had a thermoformable acoustic sheet with a measuredspatial average flow resistance of 600 Rayls, and weighed 180 g/m², witha thickness of approximately 0.5 mm.

The spacer layer had a density of 600 g/m², and consisted of a blend ofpolyester fibers with an average fiber size of 6-denier. The spacerconsisted of 30% polyester bicomponent fiber and 70% polyester staplefiber. The spatial average air flow resistance of the spacer layer wasabout 20 Rayls or approximately 1/30th the spatial average air flowresistance of the thermorformable acoustic sheet.

The wheel, fitted with the tire and the sound absorber, as describedabove, was suspended freely from a chain and allowed to gently touch anelectromagnetic shaker, which was used to excite the whole assembly. Anaccelerometer was connected to the shaker to measure the inputexcitation signal. Another accelerometer was attached to the tire, andthe transfer function was measured using 2-channel a signal analyzer.

Tests were conducted at two excitation spots on the tire and dataobtained at 16 different measuring points for each excitation spot, andthe results similarly recorded. The results of three measuring points,which are representative of the transfer functions of all of the testsconducted, are shown in FIGS. 6A, 6B and 6C. The area under the curveswas integrated to determine the total power content and was compared toa total power content measured of the tire without the in-tire silencerinstalled. By subtracting the power content in these examples, theanticipated reduction in power content, in the frequency range from zeroto 600 Hz, was then calculated.

There was a consistent reduction in the acoustic energy propagatedinside the tire. The total reduction in power content was within therange of 5.5 to 9 decibels, depending on the position of themeasurement.

Such a reduction will be translated into a reduction of vibrationalexcitation between the tire, the vehicle suspension, and the vehiclebody, resulting in an audible noise reduction within the vehicle. Theactual noise reduction within the vehicle is dependant on thesensitivity of the transmission path between the tire and the vehicleinterior.

In general, in the following claims, the terms used should not beconstrued to limit the claims to the specific embodiments disclosed inthe specification and the claims, but should be construed to include allpossible embodiments along with the full scope of equivalents to whichsuch claims are entitled. Accordingly, the claims are not limited by thedisclosure.

We claim:
 1. An in-tire sound absorber for a pneumatic wheel assemblyincluding a wheel rim and a tire fitted to the wheel rim, the soundabsorber adapted to be located within a cavity defined by the wheel rimand the tire, the sound absorber comprising a first fibrous layer and asecond fibrous layer, the second fibrous layer having a higher airflowresistance than the first fibrous layer, wherein the first fibrouslayer, the second fibrous layer, or both, is made from a non-wovenfibrous web.
 2. The sound absorber according to claim 1, wherein thefirst and second fibrous layers are made from non-woven fibrous webs. 3.The sound absorber according to claim 1 wherein the first fibrous layerhas fibers orientated substantially perpendicular to a surface of thewheel rim.
 4. The sound absorber according to claim 1, wherein the airflow resistance of the respective layers is substantially consistent toprovide a substantially constant acoustic absorption to reduce the tonalnoise.
 5. The sound absorber according to claim 1, wherein a spatialaverage of the air flow resistance of the second fibrous layer isbetween 400 and 1000 Rayls.
 6. The sound absorber according to claim 5,wherein the spatial average of the air flow resistance of the secondfibrous layer is between 600 and 800 Rayls.
 7. The sound absorberaccording to claim 1, wherein a spatial average of the flow resistivityof the first fibrous layer is in a range of 800-8000 Rayls/m.
 8. Thesound absorber according to claim 7, wherein the spatial average of theflow resistivity of the first fibrous layer is in the range of 2000-4000Rayls/m.
 9. The sound absorber according to claim 1, wherein the airflow resistance of the second fibrous layer is between 25 and 35 timesthat of the first fibrous layer.
 10. The sound absorber according toclaim 9, wherein a ratio of the air flow resistance of the secondfibrous layer to that of the first fibrous layer is approximately 30:1.11. The sound absorber according to claim 1, wherein the first fibrouslayer of the sound absorber is made from a fibrous web of polyesterfibers.
 12. The sound absorber according to claim 1, wherein the secondfibrous layer of the sound absorber is made from a fibrous web ofpolyester fibers. 13-18. (canceled)
 19. The sound absorber according toclaim 11, wherein both the first fibrous layer and the second fibrouslayer of the sound absorber are made from a fibrous web of polyesterfibers so that the sound absorber is recyclable.
 20. The sound absorberaccording to claim 1, wherein the first layer is a vertically lappedmaterial.
 21. The sound absorber according to claim 1, wherein thesecond layer is a thermoformable acoustic sheet.
 22. The sound absorberaccording to claim 1, wherein the second layer is laminated to the firstlayer.
 23. A sound absorbing system comprising: a. a tire, b. a wheelrim, the wheel rim and tire forming an enclosed tire cavity, and c. aporous insert disposed within the tire cavity comprising: a. a firstlayer comprising a vertically lapped thermally bonded nonwoven material,and b. a second fibrous layer comprising a thermoformable acousticsheet, wherein the first fibrous layer, the second fibrous layer, orboth, is made from a fibrous web of polyester fibers; wherein the secondfibrous layer has a higher air flow resistance than the first layer. 24.The sound absorbing system according to claim 23, wherein the secondiayer is laminated to the first layer with a permeable thermoplasticadhesive.
 25. The sound absorbing system according to claim 23, whereinthe porous insert reduces acoustic energy propagated inside the tire byabout 5.5 to about 9 decibels.
 26. The sound absorbing system accordingto claim 23, wherein a spatial average of the air flow resistance of thesecond layer is between 400 and 1000 Rayls, and wherein a spatialaverage of the flow resistivity of the first layer is in a range of800-8000 Rayls/m.